The bladder collects and stores urine from the kidneys and allows for discharge of the urine. The two bladder functions are controlled by the sympathetic and the parasympathetic autonomic neurological systems, and these are coordinated by the brain via the spinal cord.
The first function is to store urine in a low pressure environment without leakage. The detrusor, or bladder muscle, maintains low pressure within the bladder cavity during the storage phase. A sympathetic input prevents an increase of intravesical pressure during the accumulation of urine, and it inhibits bladder contraction. It also activates the internal sphincteric muscle (bladder neck) thus providing continence of urine.
For evacuation of the urine (micturition), the parasympathetic system causes the contraction of the detrusor muscle and the relaxation of the internal sphincter (bladder neck), thus permitting an unobstructed flow of urine.
Patients exhibit urinary symptoms due to various neurogenic (functional) or non neurogenic (anatomic) causes such as bladder outlet obstruction, overactive bladder, poor urethral support due to abnormal relaxation of the pelvic floor musculature, or sphincteric incompetence.
Urodynamic testing is a set of standard diagnostic tests used to study various urinary disorders. The testing typically includes bladder and abdominal pressure measurements, uroflows, electromyographic (EMG) signals of the external sphincter and the pelvic floor muscles, and radiographic images of the internal structure of the bladder's cavity and urethra. (See: The Bladder, Fitzpatrick, Krane, Urodynamic Studies, chapter 6, Y. Berger, pages 119–128, Churchill Livingstone, 1995; Outcomes and Obstacles of urodynamics, Contemporary Urology, Y. Berger, pages 15–31, August 1995 both of which are incorporated by reference herein). Urodynamic testing, while supplemented by electrical measurements and radiology, is primarily a system of mechanical tests. Pressure measurements are obtained via catheters that are inserted into the bladder (for intra vesical and intraabdominal pressure recordings and urethral profile pressure) or rectum (for intra abdominal pressure recordings). Uroflows are graphical and numerical data that record the stream of urine (typically measured in milliliters (ml)/sec). The EMG electrophysiological recordings are obtained from the striated external sphincteric and pelvic floor muscles and are obtained with patches (electrodes) or needles. And finally, radiographic imaging of the internal structure and contour of the bladder and its outlet can be obtained via fluoroscopic or still images during the phases of bladder storage and micturition. These measurements have standardized values that are representative of normal or abnormal bladder function.
Urodynamics, however, does not record the electromyographic activity of the smooth muscles of either the bladder (detrusor) or the internal sphincteric muscle (bladder neck). These muscles are subjected to the input of the autonomic (sympathetic and parasympathetic) neurological system. Therefore, the current evaluation of bladder function as displayed by the traditional urodynamic measurements may reflect only the outcome of mechanical pressure changes (normal or abnormal) that are the results of electrophysiological (neurogenic or myogenic) activities (normal or abnormal) that are not being assessed. For example, in the case of overactive bladder (OAB), the urodynamics will reveal evidence of involuntary detrusor contractions (IDC's) measured as abrupt bladder pressure elevations, but not disclose the cause of the IDC's. In addition, the urodynamic tests are invasive in nature, and they cannot be performed in an ambulatory setting. Urodynamic testing must be done in a clinic (office or hospital), the tests cause patient discomfort, and the data produced is artificial from a non-natural environment. Nonetheless urodynamic tests present results, primarily in the form of urodynamic graphs, that doctors and urologists are accustomed to employing in diagnosing bladder pathology.
Accordingly there is a need for a noninvasive method of measuring bladder activity for diagnosing bladder pathology and advantageously presenting the measurements in the urodynamics format familiar to doctors and urologists.